I am a professional musician (bassoon player in a symphony orchestra). I can, if I practice it a couple of times a week, achieve and sustain perfect pitch. I had no semblance of perfect pitch until I decided to practice it at age 24. Before that the only chance I had to guess a note was to put in in relation to my own voice. Even though I don't practice this anymore (it isn't very useful), I still often just instinct…
I took a music theory class in college that had a very heavy ear-training component. The TA in the course would often talk about the concept of "pitch memory", both absolute and relative. In other words, perfect pitch isn't a binary concept of you either have it or you don't, but it's your ability to remember and reproduce absolute pitches from memory. What we think of as "perfect pitch" is the extreme version of thi…
This is a function of time, not age.
Adults can (though seldom) learn languages to perfect fluency with zero accent. It's all a matter of how much time and immersion you put into it.
Adults are mostly too busy and have too many responsibilities. Children have all the time in the world.